For what, you may ask? For whatever you're writing. I have an alternative plan for what I want to do with the entry for the People's Friend serial writing competition, if it doesn't win (which is likely because I know of a few others who are entering it). I really like this story I am writing; it's a romantic mystery. I have a Plan B and a Plan C for it. If it doesn't win, then I am going to try it with Woman's Weekly as a serial. If that doesn't work, Plan C is to put it on hold and write it later on as an ebook, which I will publish myself.
You can have alternative plans for most things you write. If you write short stories for women's magazines, then have an idea which other magazine you could send it to if it's rejected. This is a v good idea as there aren't many womags out there now that take stories.
Also, you can have a Plan B for the novel you are writing. I know most authors want to have their books accepted and published by a publisher, but in this day and age it is so hard to get that. You have to have an exceptional story to be taken on. So, the alternative is to self-publish it, and these days that is easy to do. It is also more mainstream and viable. So many authors are successful with their ebooks. And it's far quicker to get out to the readers.